diff --git a/pagure/lib/model.py b/pagure/lib/model.py
index dc8ecbd..b6fbedb 100644
--- a/pagure/lib/model.py
+++ b/pagure/lib/model.py
@@ -1750,7 +1750,8 @@ class PullRequestFlag(BASE):
 
     @validates('token_id')
     def validate_token_id(self, _, token_id):
-        assert token_id is not None
+        if token_id is None:
+            raise ValueError('token_id may not be None.')
         return token_id
 
     def to_json(self, public=False):
diff --git a/tests/test_pagure_lib.py b/tests/test_pagure_lib.py
index e5fae2a..39784cc 100644
--- a/tests/test_pagure_lib.py
+++ b/tests/test_pagure_lib.py
@@ -2072,7 +2072,7 @@ class PagureLibtests(tests.Modeltests):
         self.assertEqual(len(request.flags), 0)
 
         self.assertRaises(
-            AssertionError,
+            ValueError,
             pagure.lib.add_pull_request_flag,
             session=self.session,
             request=request,